The present invention relates to a furnace for producing dental prostheses with a muffle, whereby the furnace comprises a piston driven by a drive which can be introduced into the muffle for exerting pressure onto the dental material, whereby a pressure sensor for detecting the pressure exerted by the piston is provided.
Furnaces for producing dental prostheses or dental replacement parts comprised of dental materials, especially dental ceramics, have been known for a long period of time. A plunger-type piston applies pressure onto the dental material positioned in the muffle whereby the muffle together with at least the lower portion of the piston is heated in the furnace. The furnace heats the muffle and thus the dental material for such a length of time until the dental material, under pressure applied by the piston, has completely filled the voids present in the muffle for producing the dental prostheses.
From German Patent 664 133 it is known that the inclusion formation of bubbles can be avoided when pressure is applied for an extended period of time.
The drive of the piston can be provided either by weight application or pneumatically or electrically with corresponding drive devices. For providing a cycle time as short as possible, while preventing inclusion of bubbles, it is favorable when the advancing speed of the piston is controllable. In this respect, pneumatically or electrically driven drive devices have been successfully used.
Different types of such furnaces are known. It has also been suggested already to provide an electric pressure cylinder design for driving the piston. For detecting the working pressure of the piston, the current uptake of the drive motor for the corresponding drive spindle is employed whereby, in addition, a travel/time measurement is carried out.
It is an object of the present invention to improve a muffle furnace of the aforementioned kind such that, while preventing bubble inclusion, an improved product quality of the aforementioned dental prostheses is ensured.